At the time of supplying gas to a semiconductor manufacturing chamber, a flow rate controller is inputted with, for example, an input setting flow rate of which a target value is changed stepwise, and thereby flow rate control is performed. In the past, regarding a response to such step input, how accurately an actual flow rate follows a setting flow rate in a stable state has been regarded as important as flow rate accuracy; however, in recent years, even in a transient response state, high flow rate accuracy has been additionally required.
That is, in the field of semiconductor manufacturing, an overshoot amount, a target response time required to reach a stable state from a transient response state, upper and lower limit flow rate values at each time in the transient response state, and the like are also provided with strict limitations, and therefore it is necessary to manage each flow rate controller in terms of accuracy so as to meet such required values.
In order to respond to such requirements, in a production stage of a flow rate controller, in order to adjust an individual variation among respective flow rate controllers, for example, PID parameters are adjusted on an individual flow rate controller to deliver the flow rate controller.
However, meeting required accuracy particularly in the transient response state by adjusting such control parameters has a limitation for the following reasons.
First, the adjustments of the PID parameters and the like should be made by trial and error, and in the case of attempting to strictly meet accuracy even in the transient response state, it may be difficult to make the adjustments within an adjustment time determined by restriction of production efficiency and the like.
Also, even in the case where the PID parameters can be adjusted under predetermined conditions, for example, if a parameter such as an upstream side pressure, temperature, or setting flow rate is changed, a step response also changes, and therefore the required accuracy in the transient response state may not be met. That is, by only adjusting the PID parameters, it may be difficult to keep a pattern of the step response, which is determined by the overshoot amount, target response time, and the like, within a desired range under conditions such as a setting of flow rates having different magnitudes.
Meanwhile, in addition to an approach for attempting to achieve desired flow rate accuracy by adjusting the PID parameters as described, for example, as disclosed in Patent Literature 1, there is also a method that converts an input setting flow rate inputted by a user, in which a target value changes stepwise, to a setting flow rate in which a changed target value makes it easy to obtain a preferable response, and then performs flow rate control.
Specifically, a flow rate controller described in Patent Literature 1 is one that is provided with a target value shaping part that, in the case of receiving an input setting value of which a target value changes stepwise, outputs a shaped setting flow rate in which in place of a discontinuous part, a continuously changing interval in which a target value changes rampwise is inserted, and feeds back a deviation between the shaped setting flow rate and a measured flow rate to thereby perform flow rate control.
As described, the flow rate controller attempts to, by eliminating the part where the target value discontinuously changes, and changing the target value rampwise, improve followability of an actual flow rate in a transient response.
However, even in the case of, as disclosed in Patent Literature 1, performing the flow rate control with use of the shaped setting flow rate obtained by simply replacing the discontinuous part of the input setting flow rate with a ramp function, if there is a difference in magnitude of a final target value, or the like as described above, it is difficult to meet all of constraint conditions such as a required target response time.